Base station and resource allocation method

ABSTRACT

A base station including: a memory, and a processor coupled to the memory and configure to: when scheduling a plurality of terminals based on non-orthogonal multiple access in which a same radio resource having a same time and a same frequency is allocable to two or more terminals of the plurality of terminals, calculate each metric of each of selected terminal combinations and each terminals of the plurality of terminals, each of the selected terminal combinations including two or more terminals of the plurality of terminals, and determine to allocate each radio resource to each of the selected terminal combinations and each terminals of the plurality of terminals based on each metric, wherein the selected terminal combinations are obtained by selecting, from among all terminal combinations of the plurality of terminals, each terminal combination that satisfies a first condition.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2014-194265, filed on Sep. 24,2014, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a base station deviceand a resource allocation method.

BACKGROUND

In a 3rd Generation Partnership Project Long Term Evolution (3GPP LTE)system typifying a 4th generation mobile communication system,orthogonal frequency division multiple access (OFDMA) serving as anorthogonal multiple access (OMA) scheme is used in a downlink. In theOFDMA, in the case of allocating a common time resource to users (forexample, terminals) serving as scheduling processing targets, sub-bandsthat do not interfere with one another (in other words, sub-bandsorthogonal to one another) are allocated to respective users, asillustrated in FIG. 1. FIG. 1 is a diagram made available for explainingorthogonal multiple access. In particular, in FIG. 1, resources areallocated to two users, namely, a user #1 (UE#1) and a user #2 (UE#2).If signal-to-noise ratios (SNRs) of the users #1 and #2 are SNR₁ andSNR₂, respectively, and resource allocation rates (in other words,allocated bandwidths) of the users #1 and #2 are ρ₁ and ρ₂,respectively, a “capacity (hereinafter, called a “predicted throughput”or an “expected throughput” in some cases)” of each of the users may beexpressed by the following Expression (1).

R _(k) ^((OMA))=ρ_(k) log(1+SNR_(k)), k=1,2  (1)

In contrast, in a 5th generation mobile communication system, anon-orthogonal multiple access scheme has been studied. Innon-orthogonal multiple access, in the case of allocating a common timeresource to users serving as “scheduling processing targets, sub-bandsthat interfere with one another (in other words, non-orthogonalsub-bands) are allocated to respective users. Namely, in non-orthogonalmultiple access, a same radio resource having a same time and a samefrequency is allocable to two or more terminals. In other words, asillustrated in, for example, FIG. 2, in a common sub-band, given amountsof power are distributed (allocated) to the user #1 and the user #2.FIG. 2 is a diagram made available for explaining the non-orthogonalmultiple access. In a non-orthogonal multiple access system, forexample, a communication device on a receiving side has a function (inother words, a successive interference canceller (SIC) function) ofcancelling a signal, addressed to another communication device andassigned to the same resource as that of the device of own, from areception signal and performing demodulation processing and decodingprocessing on the reception signal after the cancellation processing.

It is assumed that, as two users serving as targets of non-orthogonalmultiplexing, for example, the user #1, which is located near a basestation and whose SNR is high, and the user #2, which is located awayfrom the base station and whose SNR is low, are selected. Since the SNRof the user #2 is low, the number of modulation levels and a coding rate(in other words, a modulation and coding scheme (MCS)), applied to asignal addressed to the user #2, are lower than those applied to asignal addressed to the user #1. Therefore, it is possible for the user#1 to demodulate and decode the signal addressed to the user #2 with ahigh success probability. Accordingly, by cancelling the signaladdressed to the user #2 from a reception signal, it is possible for theuser #1 to easily remove interference from the signal addressed to theuser 2#. In other words, if it is assumed that the SNR and allocatedpower of the user #1 are SNR₁ and p₁, respectively, the capacity of theuser #1 may be expressed by the following Expression (2).

R ₁ ^((NOMA))=log(1+p ₁SNR₁)  (2)

On the other hand, the signal addressed to the user #1 becomesinterference to the signal addressed to the user #2. Accordingly, if itis assumed that the SNR and allocated power of the user #2 are SNR₂ andp₂, respectively, the capacity of the user #2 may be expressed by thefollowing Expression (3).

$\begin{matrix}{R_{2}^{({NOMA})} = {\log \left( {1 + \frac{p_{2}{SNR}_{2}}{1 + {p_{1}{SNR}_{2}}}} \right)}} & (3)\end{matrix}$

In other words, the signal addressed to the user #1 is a factor inreducing the capacity of the user #2. However, since the SNR of the user#2 is originally low, an influence on the throughput of the user #2 ishigh due to an interference noise of an another signal other than thesignal addressed to the user #1. Therefore, the influence thereon due tointerference of the signal addressed to the user #1 is low.

In this way, according to the non-orthogonal multiple access, it may beexpected that the sum of the capacities of all the users serving asmultiplexing targets (in other words, a “system capacity”) is improvedcompared with the orthogonal multiple access.

A technology of the related art is disclosed in Benjebbour A., Saito Y.,Kishiyama Y., Li A., Harada A., and Nakamura T., “Concept and practicalconsiderations of non-orthogonal multiple access (NOMA) for future radioaccess”, ISPACS 2013, November 2013.

SUMMARY

According to an aspect of the invention, a base station includes amemory, and a processor coupled to the memory and configure to: whenscheduling a plurality of terminals based on non-orthogonal multipleaccess in which a same radio resource having a same time and a samefrequency is allocable to two or more terminals of the plurality ofterminals, calculate each metric of each of selected terminalcombinations and each terminals of the plurality of terminals, each ofthe selected terminal combinations including two or more terminals ofthe plurality of terminals, and determine to allocate each radioresource to each of the selected terminal combinations and eachterminals of the plurality of terminals based on each metric, whereinthe selected terminal combinations are obtained by selecting, from amongall terminal combinations of the plurality of terminals, each terminalcombination that satisfies a first condition.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram made available for explaining orthogonal multipleaccess;

FIG. 2 is a diagram made available for explaining non-orthogonalmultiple access;

FIG. 3 is a diagram illustrating an example of a communication system ofa first embodiment;

FIG. 4 is a diagram made available for explaining a characteristic of aPF metric;

FIG. 5 is a block diagram illustrating an example of a base station ofthe first embodiment;

FIG. 6 is a block diagram illustrating an example of a scheduler of thefirst embodiment;

FIG. 7 is a block diagram illustrating an example of a metriccalculation unit of the first embodiment;

FIG. 8 is a block diagram illustrating an example of a terminal of thefirst embodiment;

FIG. 9 is a diagram made available for explaining a selection method fora metric calculation target of the first embodiment;

FIG. 10 is a diagram made available for explaining a selection methodfor a metric calculation target of the first embodiment;

FIG. 11 is a diagram made available for explaining a selection methodfor a metric calculation target of the first embodiment;

FIG. 12 is a diagram made available for explaining a selection methodfor a metric calculation target of a second embodiment;

FIG. 13 is a diagram made available for explaining a selection methodfor a metric calculation target of the second embodiment;

FIG. 14 is a diagram made available for explaining a selection methodfor a metric calculation target of the second embodiment;

FIG. 15 is a block diagram illustrating an example of a metriccalculation unit that calculates a PF metric of a combination ofterminals in a base station of a third embodiment;

FIG. 16 is a block diagram illustrating examples of a metric calculationprocessing unit and a selection unit in a base station of a fourthembodiment;

FIG. 17 is a block diagram illustrating an example of a base station ofa sixth embodiment;

FIG. 18 is a block diagram illustrating an example of a scheduler of thesixth embodiment;

FIG. 19 is a block diagram illustrating an example of a metriccalculation unit of the sixth embodiment;

FIG. 20 is a block diagram illustrating an example of a terminal of thesixth embodiment;

FIG. 21 is a diagram illustrating of an example of a hardwareconfiguration of a base station; and

FIG. 22 is a diagram illustrating of an example of a hardwareconfiguration of a terminal.

DESCRIPTION OF EMBODIMENTS

However, in non-orthogonal multiple access, there is a possibility thatthe processing amount of scheduling processing increases.

In other words, to date, in non-orthogonal multiple access, proportionalfair (PF) metrics have been calculated for individual users serving asscheduling targets and for all combinations of users. Here, a PF metricof each of the combinations of users depends on power distribution toindividual users of each of the combinations of users. Therefore, a PFmetric is calculated for each of candidates of power distribution withrespect to one combination of users and a PF metric whose value is amaximum among calculated PF metrics is used as a PF metric of the onecombination of users. In addition, a user or a combination of users,which corresponds to a maximum PF metric among the PF metrics calculatedfor the individual users serving as scheduling targets and for all thecombinations of users, is decided as a “resource allocation target”.

Since, in this way, PF metrics are repeatedly calculated for onecombination of users while changing the power distribution, a processingamount increases.

In addition, the number of combinations of users serving as calculationtargets of PF metrics increases with an increase in the number of usersserving as scheduling targets. In other words, if the number of usersserving as scheduling targets is 30, there are 435 (=₃₀C₂) combinationswhen just limited to combinations of two users. If combinations of up toN_(max) users are taken into consideration in the case where the numberof users serving as scheduling targets is K, the number of combinationsof users may be expressed by the following Expression (4).

$\begin{matrix}{\sum\limits_{i = 1}^{N_{\max}}\; {{}_{}^{}{}_{}^{}}} & (4)\end{matrix}$

The disclosed technology is made in view of the above and an objectthereof is to provide a base station device and a resource allocationmethod which are each capable of reducing a scheduling processing amountin the non-orthogonal multiple access.

Hereinafter, embodiments of a base station device and a resourceallocation method, disclosed in the present application, will bedescribed in detail, based on drawings. Note that the base stationdevice and the resource allocation method, disclosed in the presentapplication, are not limited by the embodiments. In addition, the samesymbol is assigned to a configuration having an equivalent function inembodiments and redundant description thereof will be omitted. Inaddition, the same symbol is assigned to equivalent processing steps inembodiments and the redundant description thereof will be omitted.

First Embodiment Outline of Communication System

FIG. 3 is a diagram illustrating an example of a communication system ofa first embodiment. In FIG. 3, a communication system 1 includes a basestation 10 and terminals 50-1 to 50-N_(S) (N_(S) is a natural numbergreater than or equal to two). In what follows, in the case of not beingclearly distinguished from one another, the terminals 50-1 to 50-N_(S)are collectively called terminals 50 in some cases.

In FIG. 3, the terminals 50-1 to 50-N_(S) are located within a cell C10of the base station 10. The base station 10 is a base station to whichthe non-orthogonal multiple access in which the terminals 50 aresimultaneously allocatable to a common carrier is applied. In addition,the base station 10 defines some or all of the terminals 50-1 to50-N_(S) as “scheduling targets”. Here, explanation is performed underthe assumption that all the terminals 50-1 to 50-Ns are schedulingtargets.

In addition, the base station 10 calculates PF metrics for individualterminals 50 and individual combinations of terminals, which serve as“metric calculation targets”, within the terminals 50-1 to 50-N_(S). Inaddition, based on the calculated PF metrics, the base station 10decides a terminal 50 or a combination of terminals, which serves as a“resource allocation target”, from among the “metric calculationtargets”. In addition, the base station 10 allocates a resource to theterminal 50 or the combination of terminals, which serves as a “resourceallocation target”.

Here, the base station 10 selects, as “metric calculation targets”, theindividual terminals 50 serving as “scheduling processing targets”. Fromamong all the combinations of terminals within the terminals 50-1 to50-N_(S) serving as the “scheduling processing targets”, the basestation 10 selects, as the “metric calculation targets”, combinations ofterminals, which satisfy a “first condition”, and excludes combinationsof terminals, which do not satisfy the “first condition”, from the“metric calculation targets”. The “first condition” includes a conditionthat, regarding a combination of terminals including, for example, afirst terminal 50 and a second terminal 50, a ratio (hereinafter, calleda “first ratio” in some cases) of an average throughput of the firstterminal 50 to an average throughput of the second terminal 50 is largerthan a “first threshold value” and is smaller than a “second thresholdvalue”.

From this, combinations of terminals that do not satisfy the “firstcondition” are excluded from the “metric calculation targets”.Therefore, it is possible to reduce the number of metric calculationtargets, and as a result, it is possible to reduce a schedulingprocessing amount in the non-orthogonal multiple access.

A PF metric of a combination of users (in the case of two terminals)will be considered. It is assumed that a user whose “instantaneous SNR”is high is the user #1 and a user whose “instantaneous SNR” is low isthe user #2. It is assumed that the instantaneous SNRs of the user #1and the user #2 are γ₁ and γ₂, respectively, and the average throughputsof the user #1 and the user #2 are T₁ and T₂, respectively. In addition,it is assumed that allocated power for the user #1 is p₁, allocatedpower for the user #2 is p₂, and total power (in other words, p₁+p₂) is“1”. At this time, the PF metric of this combination of users may beexpressed by the following Expression (5).

$\begin{matrix}{{{g\left( {p_{1},p_{2}} \right)} = {{T_{1}^{- 1}{\log \left( {1 + {p_{1}\gamma_{1}}} \right)}} + {T_{2}^{- 1}{\log \left( {1 + \frac{p_{2}\gamma_{2}}{1 + {p_{1}\gamma_{2}}}} \right)}}}},{{p_{1} + p_{2}} = 1},{p_{1} \geq 0},{p_{2} \geq 0}} & (5)\end{matrix}$

In Expression (5), if p₂ is erased using a condition of p₁+p₂=1, thefollowing Expression (6) may be derived.

$\begin{matrix}{{{g\left( p_{1} \right)} = {{T_{1}^{- 1}{\log \left( {1 + {p_{1}\gamma_{1}}} \right)}} + {T_{2}^{- 1}{\log \left( {1 + \frac{\left( {1 - p_{1}} \right)\gamma_{2}}{1 + {p_{1}\gamma_{2}}}} \right)}}}},{0 \leq p_{1} \leq 1}} & (6)\end{matrix}$

Here, if it is assumed that γ₁=10 dB and γ₂=0 dB are satisfied, the PFmetric of a combination of users (in the case of two terminals) has avalue illustrated in FIG. 4 (the optimal point in FIG. 4) in accordancewith the allocated power p₁ for the user #1 and a ratio (T₁/T₂) of theaverage throughput of the user #1 to the average throughput of the user#2. FIG. 4 is a diagram made available for explaining a characteristicof a PF metric. As may be seen from FIG. 4, in the case where theabove-mentioned “first ratio”, in other words, the ratio (T₁/T₂) of theaverage throughput of the user #1 to the average throughput of the user#2 is less than or equal to a first predetermined value (correspondingto the above-mentioned “first threshold value”) R₁, the optimal value ofp₁ where the PF metric becomes a maximum is “1”. In other words, it isrevealed that, in the case where the average throughput ratio is lessthan or equal to the first predetermined value, in this usercombination, it is preferable to allocate the total amount of power tothe user #1 rather than performing the non-orthogonal multiplexing.

On the other hand, in the case where the average throughput ratio isgreater than or equal to a second predetermined value (corresponding tothe above-mentioned “second threshold value”) R₂, the optimal value ofp₁ where the PF metric becomes a maximum is “0”. In other words, it isrevealed that, in the case where the average throughput ratio is greaterthan or equal to the second predetermined value, in this usercombination, it is preferable to allocate the total amount of power tothe user #2 rather than performing non-orthogonal multiplexing.

Accordingly, in the case where the average throughput ratio is less thanor equal to the first predetermined value or is greater than or equal tothe second predetermined value, if the PF metric of each of the user #1and the user #2 is a “metric calculation target”, it is possible toexclude the user combination of the user #1 and the user #2 from the“metric calculation targets”.

Example of Configuration of Base Station

FIG. 5 is a block diagram illustrating an example of a base station ofthe first embodiment. In FIG. 5, the base station 10 includes user datasignal generation units 11-1 to 11-N_(S), a multiplexing unit 12, achannel multiplexing unit 13, an OFDM transmission processing unit 14,and a wireless transmission unit 15. In addition, the base station 10includes a wireless reception unit 16, a reception processing unit 17,an extraction unit 18, a scheduler 19, and a control signal generationunit 20.

The user data signal generation units 11-1 to 11-N_(S) correspond to theterminals 50-1 to 50-N_(S), respectively, which serve as schedulingtargets. Upon receiving “scheduling information” from the scheduler 19,each of the user data signal generation units 11 generates a user datasignal, based on the scheduling information. The “schedulinginformation” includes the number of modulation levels, a coding rate,and a power value. As described later, the user data signals generatedin the respective user data signal generation units 11 that each receivethe scheduling information in the same time period become targets of thenon-orthogonal multiple access. Here, it is assumed that a maximum valueof a non-orthogonal multiplex number is N_(max). N_(max) is a naturalnumber less than or equal to N_(S).

As illustrated in, for example, FIG. 5, the user data signal generationunits 11 each include, for example, a coding unit 21, a modulation unit22, and a power adjustment unit 23. The coding unit 21 performs errorcorrection coding processing on user data in accordance with the codingrate included in the scheduling information and outputs an obtained datasequence to the modulation unit 22. The modulation unit 22 performsmodulation processing on the data sequence received from the coding unit21 and outputs an obtained modulation signal to the power adjustmentunit 23. The power adjustment unit 23 adjusts the power of themodulation signal received from the modulation unit 22 and outputs, tothe multiplexing unit 12, a signal after the power adjustment, as theuser data signal.

The multiplexing unit 12 receives, in the same time period, user datasignals from the up to N_(max) user data signal generation units 11 andmultiplexes the received data signals. In other words, the multiplexingunit 12 superimposes the received data signals and maps a superimposedsignal to a predetermined subcarrier. In addition, the multiplexing unit12 outputs an obtained multiplexed signal to the channel multiplexingunit 13.

The channel multiplexing unit 13 multiplexes a control signal receivedfrom the control signal generation unit 20 and the multiplexed signalreceived from the multiplexing unit 12. Here, not the non-orthogonalmultiplexing but orthogonal multiplexing (in other words, timemultiplexing, frequency multiplexing, or code multiplexing) is used. Inaddition, the channel multiplexing unit 13 outputs the obtainedmultiplexed signal to the OFDM transmission processing unit 14.

The OFDM transmission processing unit 14 generates an OFDM signal fromthe multiplexed signal received from the multiplexing unit 13. Asillustrated in FIG. 5, the OFDM transmission processing unit 14 includesan inverse fast Fourier transform (IFFT) unit 25 and a cyclic prefix(CP) addition unit 26. The IFFT unit 25 converts the multiplexed signalreceived from the channel multiplexing unit 13 from a signal in afrequency domain to a signal in a time domain. In addition, by adding aCP to the signal in the time domain, obtained in the IFFT unit 25, theCP addition unit 26 obtains the OFDM signal.

The wireless transmission unit 15 performs predetermined wirelesstransmission processing (digital-to-analog conversion, up-conversion,amplification, and so forth) on the OFDM signal obtained in the OFDMtransmission processing unit 14 and transmits an obtained wirelesssignal via an antenna.

The wireless reception unit 16 performs predetermined wireless receptionprocessing (down-conversion, analog-to-digital conversion, and so forth)on a wireless signal received via an antenna and outputs an obtainedsignal to the reception processing unit 17.

The reception processing unit 17 performs predetermined receptionprocessing (demodulation, decoding, and so forth) on the signal receivedfrom the wireless reception unit 16 and outputs obtained reception datato the extraction unit 18.

The extraction unit 18 extracts, from the reception data received fromthe reception processing unit 17, control data (Ack/Nack, channel stateinformation (including a channel quality indicator (CQI), a precodingmatrix indicator (PMI), a rank indicator (RI), and so forth) and outputsthe extracted control data to the scheduler 19.

The control signal generation unit 20 generates a control signalincluding “control information” received from the scheduler 19 andoutputs the generated control signal to the channel multiplexing unit13. The “control information” includes identification information ofeach of users serving as targets of the non-orthogonal multiplexing, acoding rate applied to a user data signal addressed to each of theusers, the number of modulation levels, an adjusted power value, and soforth.

For each of the terminals 50 and combinations of terminals, which servesas a “metric calculation target” within the terminals 50-1 to 50-N_(S)serving as the “scheduling processing targets”, the scheduler 19calculates a PF metric. In addition, based on the calculated PF metrics,the scheduler 19 decides a terminal 50 or a combination of terminals,which serves as a “resource allocation target”, from among the “metriccalculation targets”. In addition, the scheduler 19 allocates a resourceto the terminal 50 or the combination of terminals, which serves as the“resource allocation target”.

Here, the scheduler 19 defines, as the “metric calculation targets”, theindividual terminals 50 serving as the “scheduling processing targets”.In addition, from among all the combinations of terminals within theterminals 50-1 to 50-N_(S) serving as the “scheduling processingtargets”, the scheduler 19 selects, as the “metric calculation targets”,combinations of terminals, which satisfy the “first condition”, andexcludes combinations of terminals, which do not satisfy the “firstcondition”, from the “metric calculation targets”.

As illustrated in, for example, FIG. 6, the scheduler 19 includes anaverage throughput calculation unit 31, an instantaneous SNR calculationunit 32, a metric calculation unit 33, an allocation decision unit 34,and an MCS decision unit 35. FIG. 6 is a block diagram illustrating anexample of a scheduler of the first embodiment.

The average throughput calculation unit 31 calculates the averagethroughput of each of the terminals 50 serving as the schedulingprocessing targets and outputs the calculated average throughput of eachof the terminals 50 to the metric calculation unit 33.

The instantaneous SNR calculation unit 32 calculates the instantaneousSNR of each of the terminals 50 serving as the scheduling processingtargets and outputs, to the metric calculation unit 33, the calculatedinstantaneous SNR of each of the terminals 50. The calculation of theinstantaneous SNR is performed based on the channel state informationtransmitted from each of the terminals 50.

For each of the terminals 50 and combinations of terminals, which servesas a “metric calculation target” within the terminals 50-1 to 50-N_(S)serving as the “scheduling processing targets”, the metric calculationunit 33 calculates a PF metric. In addition, from among all thecombinations of terminals within the terminals 50-1 to 50-N_(S) servingas the “scheduling processing targets”, the metric calculation unit 33selects, as the “metric calculation targets”, combinations of terminals,which satisfy the “first condition”, in addition to the individualterminals 50 of the terminals 50-1 to 50-N_(S) serving as the“scheduling processing targets”. On the other hand, the metriccalculation unit 33 excludes combinations of terminals, which do notsatisfy the “first condition”, from the “metric calculation targets”.

As illustrated in, for example, FIG. 7, the metric calculation unit 33includes a metric calculation processing unit 41, a metric calculationprocessing unit 42, and a selection unit 43. FIG. 7 is a block diagramillustrating an example of a metric calculation unit of the firstembodiment.

Using the average throughput received from the average throughputcalculation unit 31 and the instantaneous SNR received from theinstantaneous SNR calculation unit 32, the metric calculation processingunit 41 calculates the PF metric of each of the terminals 50 serving asthe scheduling processing targets. In other words, usually each of theterminals 50 serving as the scheduling processing targets is defined asa calculation target of the PF metric.

Using, for example, the following Expression (7), the metric calculationprocessing unit 41 calculates the PF metric of each of the terminals 50.

f ⁽¹⁾(k)=T _(k) ⁻¹ log(1+γ_(k)), k=1,2, . . . ,K  (7)

Here, T_(k) is the average throughput of a k-th user and γ_(k) is theinstantaneous SNR of the k-th user.

From among all the combinations of terminals, in each of which thenumber of component terminals is up to N_(max) within the terminals 50-1to 50-N_(S) serving as the “scheduling processing targets”, theselection unit 43 selects, as the “metric calculation targets”,combinations of terminals, which satisfy the “first condition”, andexcludes combinations of terminals, which do not satisfy the “firstcondition”, from the “metric calculation targets”.

For each of the combinations of terminals that serve as the “metriccalculation targets” and are selected in the selection unit 43, themetric calculation processing unit 42 calculates the PF metric. In otherwords, regarding each of the combinations of terminals serving as the“metric calculation targets”, the metric calculation processing unit 42calculates the PF metric for each of candidates of power distributionand defines, as the PF metric of each of the combinations of terminals,a PF metric whose value is a maximum among the calculated PF metrics.

In other words, for each combination s(m) of terminals included in a setS(m) (in this regard, however, m=2 to N_(max)) of the combinations ofterminals that serve as the “metric calculation targets” and that areoutput from the selection unit 43, the metric calculation processingunit 42 decides the PF metric and optimal power distribution in thiscombination of terminals. This is a maximization problem illustrated inthe following Expression (8) and may be solved using an “iterativewater-filling algorithm” of the related art.

$\begin{matrix}{{{{maximize}\mspace{14mu} {f(s)}} = {\sum\limits_{k \in s^{(m)}}\; {T_{k}^{- 1}{\log\left( {1 + \frac{p_{k}\gamma_{k}}{1 + {\gamma_{k}{\sum\limits_{j = 1}^{k - 1}\; p_{j}}}}} \right)}}}}{{{{subject}\mspace{14mu} {to}\mspace{14mu} {\sum\limits_{k = 1}^{m}\; p_{k}}} = 1},{p_{k} \geq 0},{k = 1},2,\ldots \mspace{14mu},m}{s^{(m)} \in S^{(m)}}} & (8)\end{matrix}$

Here, the above-mentioned “first condition” is illustrated as follows.

In other words, in the case of two-user multiplexing, the “firstcondition” includes a condition that the following Expression (9) issatisfied.

$\begin{matrix}{\frac{\gamma_{1}\left( {1 + \gamma_{2}} \right)}{\gamma_{2}\left( {1 + \gamma_{1}} \right)} < \frac{T_{1}}{T_{2}} < \frac{\gamma_{1}}{\gamma_{2}}} & (9)\end{matrix}$

Here, it is assumed that a user whose instantaneous SNR is high is theuser #1 and a user whose instantaneous SNR is low is the user #2. It isassumed that the instantaneous SNRs of the user #1 and the user #2 areγ₁ and γ₂, respectively, and the average throughputs of the user #1 andthe user #2 are T₁ and T_(z), respectively.

In addition, in the case of three-user multiplexing, the “firstcondition” includes a condition that both the above-mentioned Expression(9) and the following Expression (10) are satisfied.

$\begin{matrix}{\frac{\gamma_{2}\left( {1 + \gamma_{3}} \right)}{\gamma_{3}\left( {1 + \gamma_{2}} \right)} < \frac{T_{2}}{T_{3}} < \frac{\gamma_{2}}{\gamma_{3}}} & (10)\end{matrix}$

Here, it is assumed that the instantaneous SNR becomes reduced in valuein the order of the user #1, the user #2, and the user #3. It is assumedthat the instantaneous SNR and the average throughput of the user #3 areγ₃ and T₃, respectively.

In addition, in the case of m-user multiplexing whose rank is higherthan or equal to four-user multiplexing, the “first condition” includesa condition that the following Expression (11) is satisfied.

$\begin{matrix}{\frac{\gamma_{m - 1}\left( {1 + \gamma_{m}} \right)}{\gamma_{m}\left( {1 + \gamma_{m - 1}} \right)} < \frac{T_{m - 1}}{T_{m}} < \frac{\gamma_{m - 1}}{\gamma_{m}}} & (11)\end{matrix}$

Here, it is assumed that the instantaneous SNR becomes reduced in valuein the order of the user #1, the user #2, . . . and the user #m. It isassumed that the instantaneous SNR and the average throughput of theuser #m are γ_(m) and T_(m), respectively.

Next, a derivation process of the above-mentioned “first condition” willbe described.

On Two-User Multiplexing

First, the derivation process of the “first condition” in the case ofthe two-user multiplexing will be described.

In the case of the two-user multiplexing, the PF metric may be expressedby the following Expression (12).

$\begin{matrix}{{{f\left( {p_{1},p_{2}} \right)} = {{T_{1}^{- 1}{\log \left( {1 + {p_{1}\gamma_{1}}} \right)}} + {T_{2}^{- 1}{\log \left( {1 + \frac{p_{2}\gamma_{2}}{1 + {p_{1}\gamma_{2}}}} \right)}}}},{{p_{1} + p_{2}} = 1},{p_{1} \geq 0},{p_{2} \geq 0}} & (12)\end{matrix}$

If being converted to a form of one variable, based on p₁+p₂=1,Expression (12) is expressed by the following Expression (13).

$\begin{matrix}{{{f\left( p_{1} \right)} = {{T_{1}^{- 1}{\log \left( {1 + {p_{1}\gamma_{1}}} \right)}} + {T_{2}^{- 1}\log \left( {1 + \frac{\left( {1 + p_{1}} \right)\gamma_{2}}{1 + {p_{1}\gamma_{2}}}} \right)}}},{0 \leq p_{1} \leq 1}} & (13)\end{matrix}$

Since it is certain that a derivative be positive in order for f(p₁) tobe a monotonically increasing function, the following Expression (14) isderived.

$\begin{matrix}{{\frac{\partial{f\left( p_{1} \right)}}{\partial p_{1}} = {{{T_{1}^{- 1}\frac{\gamma_{1}}{1 + {p_{1}\gamma_{1}}}} - {T_{2}^{- 1}\frac{\gamma_{2}}{1 + {p_{1}\gamma_{2}}}}} \geq 0}}{{\frac{T_{1}}{T_{2}} \leq \frac{\gamma_{1}\left( {1 + {p_{1}\gamma_{2}}} \right)}{\gamma_{2}\left( {1 + {p_{1}\gamma_{1}}} \right)}} = {h\left( p_{1} \right)}}} & (14)\end{matrix}$

As illustrated in the following Expression (15), h(p₁) in Expression(14) is a monotonically decreasing function.

$\begin{matrix}{\frac{\partial{h\left( p_{1} \right)}}{\partial p_{1}} = {{\frac{\gamma_{1}}{\gamma_{2}}\frac{\gamma_{2} - \gamma_{1}}{\left( {1 + {p_{1}\gamma_{1}}} \right)^{2}}} \leq {0\mspace{14mu} \left( {\because{\gamma_{1} \geq \gamma_{2}}} \right)}}} & (15)\end{matrix}$

Accordingly, if a condition expressed by the following Expression (16)is satisfied, the f(p₁) becomes a monotonically increasing function. Inthis regard, however, min(x) indicates a minimum value of x.

$\begin{matrix}{{\frac{T_{1}}{T_{2}} \leq {\min \left( \frac{\gamma_{1}\left( {1 + {p_{1}\gamma_{2}}} \right)}{\gamma_{2}\left( {1 + {p_{1}\gamma_{1}}} \right)} \right)}} = {{h\left( {p_{1} = 1} \right)} = \frac{\gamma_{1}\left( {1 + \gamma_{2}} \right)}{\gamma_{2}\left( {1 + \gamma_{1}} \right)}}} & (16)\end{matrix}$

By contrast, since it is certain that a derivative be negative in orderfor f(p₁) to be a monotonically decreasing function, the followingExpression (17) is derived.

$\begin{matrix}{{\frac{T_{1}}{T_{2}} \geq \frac{\gamma_{1}\left( {1 + {p_{1}\gamma_{2}}} \right)}{\gamma_{2}\left( {1 + {p_{1}\gamma_{1}}} \right)}} = {h\left( p_{1} \right)}} & (17)\end{matrix}$

Accordingly, if a condition expressed by the following Expression (18)is satisfied, f(p₁) becomes a monotonically decreasing function. In thisregard, however, max(x) indicates a maximum value of x.

$\begin{matrix}{{\frac{T_{1}}{T_{2}} \geq {\max \left( \frac{\gamma_{1}\left( {1 + {p_{1}\gamma_{2}}} \right)}{\gamma_{2}\left( {1 + {p_{1}\gamma_{1}}} \right)} \right)}} = {{h\left( {p_{1} = 0} \right)} = \frac{\gamma_{1}}{\gamma_{2}}}} & (18)\end{matrix}$

In the case where the PF metric becomes a monotonically increasingfunction in this way, even if the non-orthogonal multiplexing isperformed in this user combination, the PF metric thereof does notexceed a PF metric in the case where allocation is only performed on theuser #1. In the case where, in an opposite manner, the PF metric becomesa monotonically decreasing function, even if the non-orthogonalmultiplexing is performed in this user combination, the PF metricthereof does not exceed a PF metric in the case where allocation is onlyperformed on the user #2.

From the above, by combining Expression (16) and Expression (18), thecondition illustrated in Expression (9) is derived.

On Three-User Multiplexing

Next, the derivation process of the “first condition” in the case of thethree-user multiplexing will be described.

In the case of the three-user multiplexing, the PF metric may beexpressed by the following Expression (19).

$\begin{matrix}{{{f\left( {p_{1},p_{2},p_{3}} \right)} = {{T_{1}^{- 1}{\log \left( {1 + {p_{1}\gamma_{1}}} \right)}} + {T_{2}^{- 1}{{\log \left( {1 + \frac{p_{2}\gamma_{2}}{1 + {p_{1}\gamma_{2}}}} \right)} \cdot T_{3}^{- 1}}{\log \left( {1 + \frac{p_{3}\gamma_{3}}{1 + {p_{1}\gamma_{3}} + {p_{2}\gamma_{3}}}} \right)}}}},\mspace{20mu} {{\sum\limits_{k = 1}^{3}\; p_{k}} - 1},{p_{k} \geq 0},{k = 1},2,3} & (19)\end{matrix}$

If p₃ in Expression (19) is erased, Expression (19) is expressed by thefollowing Expression (20).

$\begin{matrix}{{{f\left( {p_{1},p_{2}} \right)} = {{T_{1}^{- 1}{\log \left( {1 + {p_{1}\gamma_{1}}} \right)}} + {T_{2}^{- 1}{\log \left( {1 + \frac{p_{2}\gamma_{2}}{1 + {p_{1}\gamma_{2}}}} \right)}} + {T_{3}^{- 1}{\log \left( {1 + \frac{\left( {1 - p_{1} - p_{2}} \right)\gamma_{3}}{1 + {p_{1}\gamma_{3}} + {p_{2}\gamma_{3}}}} \right)}}}}\mspace{20mu} {{{p_{1} + p_{2}} < 1},{p_{1} \geq 0},{p_{2} \geq 0}}} & (20)\end{matrix}$

If Expression (20) is partially differentiated with respect to p₂, thefollowing Expression (21) is obtained.

$\begin{matrix}{{\frac{\partial}{\partial p_{2}}{f\left( {p_{1},p_{2}} \right)}} = {{T_{2}^{- 1}\frac{\gamma_{2}}{1 + {\left( {p_{1} + p_{2}} \right)\gamma_{2}}}} - {T_{3}^{- 1}\frac{\gamma_{3}}{1 + {\left( {p_{1} + p_{2}} \right)\gamma_{3}}}}}} & (21)\end{matrix}$

It is certain that a partial derivative with respect to p₂ be positivein order for the PF metric expressed by Expression (20) to be amonotonically increasing function with respect to p₂ in the case offixing p₁. Therefore, the following Expression (22) is derived.

$\begin{matrix}{{\frac{\partial}{\partial p_{2}}{f\left( {p_{1},p_{2}} \right)}} = {{{T_{2}^{- 1}\frac{\gamma_{2}}{1 + {\left( {p_{1} + p_{2}} \right)\gamma_{2}}}} - {T_{3}^{- 1}\frac{\gamma_{3}}{1 + {\left( {p_{1} + p_{2}} \right)\gamma_{3}}}}} > 0}} & (22)\end{matrix}$

If Expression (22) is deformed, Expression (23) is derived.

$\begin{matrix}{\frac{T_{2}}{T_{3}} < \frac{\gamma_{2}\left\{ {1 + {\left( {p_{1} + p_{2}} \right)\gamma_{3}}} \right\}}{\gamma_{3}\left\{ {1 + {\left( {p_{1} + p_{2}} \right)\gamma_{2}}} \right\}}} & (23)\end{matrix}$

If Expression (23) is regarded as a function of p₁₂ (=p₁+p₂), thefollowing Expression (24) is derived.

$\begin{matrix}{{{h\left( p_{12} \right)} = \frac{\gamma_{2}\left( {1 + {p_{12}\gamma_{3}}} \right)}{\gamma_{3}\left( {1 + {p_{12}\gamma_{2}}} \right)}}{p_{12} = {p_{1} + p_{2}}}} & (24)\end{matrix}$

As illustrated in the following Expression (25), h(p₁₂) is amonotonically decreasing function.

$\begin{matrix}{\frac{{h\left( p_{12} \right)}}{p_{12}} = {{\frac{\gamma_{2}}{\gamma_{3}}\frac{\gamma_{3} - \gamma_{2}}{\left( {1 + {p_{12}\gamma_{2}}} \right)^{2}}} \leq {0\mspace{31mu} \left( {\because{\gamma_{2} \geq \gamma_{3}}} \right)}}} & (25)\end{matrix}$

Accordingly, if a condition expressed by the following Expression (26)is satisfied, the partial derivative with respect to p₂ becomes positiveand f(p₁,p₂) becomes a monotonically increasing function with respect top₂ in the case of fixing p₁. In other words, p₃=0 is an optimal value.

$\begin{matrix}{{\frac{T_{2}}{T_{3}} \leq {\min \left\{ {h\left( {p_{1} + p_{2}} \right)} \right\}}} = {{a\left( {{p_{1} + p_{2}} = 1} \right)} = \frac{\gamma_{2}\left( {1 + \gamma_{3}} \right)}{\gamma_{3}\left( {1 + \gamma_{2}} \right)}}} & (26)\end{matrix}$

In other words, even if non-orthogonal multiplexing is performed in thiscombination of three users, the PF metric thereof does not exceed the PFmetric in the non-orthogonal multiplexing of the combination of twousers based on the user #1 and the user #2. Accordingly, it is possibleto exclude this combination of three users from the metric calculationtargets.

On the other hand, if a condition expressed by the following Expression(27) is satisfied, the partial derivative with respect to p₂ becomesnegative and f(p₁,p₂) becomes a monotonically decreasing function withrespect to p₂ in the case of fixing p₁. In other words, p₂=0 is anoptimal value. In other words, it is most appropriate to allocate totalpower to the user #1 and the user #3.

$\begin{matrix}{{\frac{T_{2}}{T_{3}} \geq {\max \left\{ {h\left( {p_{1} + p_{2}} \right)} \right\}}} = {{a\left( {{p_{1} + p_{2}} = 0} \right)} = \frac{\gamma_{2}}{\gamma_{3}}}} & (27)\end{matrix}$

In other words, even if non-orthogonal multiplexing is performed in thiscombination of three users, the PF metric thereof does not exceed the PFmetric in the non-orthogonal multiplexing of the combination of twousers based on the user #1 and the user #3. Accordingly, it is possibleto exclude the PF metric in this combination of three users from themetric calculation targets.

Next, if p₂ in Expression (19) is erased, Expression (19) is expressedby the following Expression (28).

$\begin{matrix}{{f\left( {p_{1},p_{3}} \right)} = {{T_{1}^{- 1}{\log \left( {1 + {p_{1}\gamma_{1}}} \right)}} + {T_{2}^{- 1}{\log \left( {1 + \frac{\left( {1 - p_{1} - p_{3}} \right)\gamma_{2}}{1 + {p_{1}\gamma_{2}}}} \right)}} + {T_{3}^{- 1}{\log \left( {1 + \frac{p_{3}\gamma_{3}}{1 + {\left( {1 - p_{3}} \right)\gamma_{e}}}} \right)}}}} & (28) \\{\mspace{79mu} {{{p_{1} + p_{3}} \leq 1},\mspace{14mu} {p_{1} \geq 0},\mspace{14mu} {p_{3} \geq 0}}} & \;\end{matrix}$

If Expression (28) is partially differentiated with respect to p₃, thefollowing Expression (29) is obtained.

$\begin{matrix}{{\frac{\partial}{\partial p_{1}}{f\left( {p_{1},p_{3}} \right)}} = {{T_{1}^{- 1}\frac{\gamma_{1}}{1 + {p_{1}\gamma_{1}}}} - {T_{2}^{- 1}\frac{\gamma_{2}}{1 + {p_{1}\gamma_{2}}}}}} & (29)\end{matrix}$

It is certain that a partial derivative with respect to p₁ be positivein order for the PF metric expressed by Expression (28) to be amonotonically increasing function with respect to p₁ in the case offixing p₃. Therefore, the following Expression (30) is derived.

$\begin{matrix}{\frac{T_{1}}{T_{2}} \leq \frac{\gamma_{1}\left( {1 + {p_{1}\gamma_{2}}} \right)}{\gamma_{2}\left( {1 + {p_{1}\gamma_{1}}} \right)}} & (30)\end{matrix}$

If Expression (30) is regarded as a function of p₁, the followingExpression (31) is derived.

$\begin{matrix}{{h\left( p_{1} \right)} = \frac{\gamma_{1}\left( {1 + {p_{1}\gamma_{2}}} \right)}{\gamma_{2}\left( {1 + {p_{1}\gamma_{1}}} \right)}} & (31)\end{matrix}$

As illustrated in the following Expression (32), h(p₁) is amonotonically decreasing function.

$\begin{matrix}{{\frac{\partial}{\partial p_{1}}{h\left( p_{1} \right)}} = {{\frac{\gamma_{1}}{\gamma_{2}}\frac{\gamma_{2} - \gamma_{1}}{\left( {1 + {p_{1}\gamma_{1}}} \right)^{2}}} \leq {0\mspace{31mu} \left( {\because{\gamma_{1} \geq \gamma_{2}}} \right)}}} & (32)\end{matrix}$

Accordingly, if a condition expressed by the following Expression (33)is satisfied, f(p₁,p₃) becomes a monotonically increasing function withrespect to p₁ in the case of fixing p₃. In other words, p₂=0 is anoptimal value.

$\begin{matrix}{{\frac{T_{1}}{T_{2}} \leq {\min \left( \frac{\gamma_{1}\left( {1 + {p_{1}\gamma_{2}}} \right)}{\gamma_{2}\left( {1 + {p_{1}\gamma_{1}}} \right)} \right)}} = {{h\left( {p_{1} = 1} \right)} = \frac{\gamma_{1}\left( {1 + \gamma_{2}} \right)}{\gamma_{2}\left( {1 + \gamma_{1}} \right)}}} & (33)\end{matrix}$

In addition, it is certain that the partial derivative with respect top₁ be negative in order for f(p₁,p₃) to be a monotonically decreasingfunction with respect to p₁. Therefore, if a condition of the followingExpression (34) is satisfied, f(p₁,p₃) becomes a monotonicallydecreasing function with respect to p₁ in the case of fixing p₃. Inother words, p₁=0 is an optimal value.

$\begin{matrix}{{\frac{T_{1}}{T_{2}} \geq {\max \left( \frac{\gamma_{1}\left( {1 + {p_{1}\gamma_{2}}} \right)}{\gamma_{2}\left( {1 + {p_{1}\gamma_{1}}} \right)} \right)}} = {{h\left( {p_{1} = 0} \right)} = \frac{\gamma_{1}}{\gamma_{2}}}} & (34)\end{matrix}$

From the above, a condition that both the above-mentioned Expression (9)and the following Expression (10) are satisfied is derived.

On m-User Multiplexing whose Rank Is Higher than or Equal to Four-UserMultiplexing

Next, the derivation process of the “first condition” in the case ofm-user multiplexing whose rank is higher than or equal to four-usermultiplexing will be described.

In the case of the m-user multiplexing whose rank is higher than orequal to four-user multiplexing, the PF metric may be expressed by thefollowing Expression (35).

$\begin{matrix}{{{f\left( {p_{1},p_{2},\ldots \mspace{14mu},p_{m}} \right)} = {\sum\limits_{k = 1}^{m}{T_{k}^{- 1}{\log\left( {1 + \frac{p_{k}\gamma_{k}}{1 + {\gamma_{k}{\sum\limits_{j = 1}^{k - 1}p_{j}}}}} \right)}}}}{{{\sum\limits_{k = 1}^{m}p_{k}} = 1},\mspace{14mu} {p_{k} \geq 0},\mspace{14mu} {k = 1},2,\ldots \mspace{14mu},m}} & (35)\end{matrix}$

If p_(m) in Expression (35) is erased, Expression (35) is expressed bythe following Expression (36).

$\begin{matrix}{{f\left( {p_{1},p_{2},\ldots \mspace{14mu},p_{m\mspace{11mu} 1}} \right)} = {{\sum\limits_{k = 1}^{m - 1}{T_{k}^{- 1}{\log\left( {1 + \frac{p_{k}\gamma_{k}}{1 + {\gamma_{k}{\sum\limits_{j = 1}^{k - 1}p_{j}}}}} \right)}}} + {T_{m}^{- 1}{\log\left( {1 + \frac{\left( {1 - {\sum\limits_{j = 1}^{m - 1}p_{j}}} \right)\gamma_{m}}{1 + {\gamma_{m}{\sum\limits_{j = 1}^{m - 1}p_{j}}}}} \right)}}}} & (36) \\{\mspace{79mu} {{{\sum\limits_{k = 1}^{m - 1}p_{k}} \leq 1},\mspace{14mu} {p_{k} \geq 0},\mspace{14mu} {k = 1},2,\ldots \mspace{14mu},{m - 1}}} & \;\end{matrix}$

If Expression (36) is partially differentiated with respect to p_(m-1),the following Expression (37) is obtained.

$\begin{matrix}{{\frac{\partial}{\partial p_{m - 1}}{f\left( {p_{1},p_{2},\ldots \mspace{14mu},p_{m - 1}} \right)}} = {{T_{m - 1}^{- 1}\frac{\gamma_{m - 1}}{1 + {\gamma_{m - 1}{\sum\limits_{j = 1}^{m - 1}p_{j}}}}} - {T_{m}^{- 1}\frac{\gamma_{m}}{1 + {\gamma_{m}{\sum\limits_{j = 1}^{m - 1}p_{j}}}}}}} & (37)\end{matrix}$

It is certain that a partial derivative with respect to p_(m-1) bepositive in order for the PF metric expressed by Expression (35) to be amonotonically increasing function with respect to p_(m-1). Therefore,the following Expression (38) is derived.

$\begin{matrix}{\frac{T_{m - 1}}{T_{m}} \leq \frac{\gamma_{m - 1}\left( {1 + {\gamma_{m}{\sum\limits_{j = 1}^{m - 1}p_{j}}}} \right)}{\gamma_{m}\left( {1 + {\gamma_{m - 1}{\sum\limits_{j = 1}^{m - 1}p_{j}}}} \right)}} & (38)\end{matrix}$

If Expression (38) is regarded as a function of total power of usersother than a user #m, the following Expression (39) is derived.

$\begin{matrix}{{h\left( {\sum\limits_{j = 1}^{m - 1}p_{j}} \right)} = \frac{\gamma_{m - 1}\left( {1 + {\gamma_{m}{\sum\limits_{j = 1}^{m - 1}p_{j}}}} \right)}{\gamma_{m}\left( {1 + {\gamma_{m - 1}{\sum\limits_{j = 1}^{m - 1}p_{j}}}} \right)}} & (39)\end{matrix}$

Expression (39) is a monotonically decreasing function with respect tothe total power of users other than the user #m. Accordingly, if acondition expressed by the following Expression (40) is satisfied, thePF metric illustrated in Expression (36) becomes a monotonicallyincreasing function with respect to p_(m-1) in the case of fixing p₁ top_(m-2). In other words, p_(m)=0 is an optimal value. In other words, itis most appropriate to allocate total power to the user #1 to a user#m−1.

$\begin{matrix}{{\frac{T_{m - 1}}{T_{m}} \leq {\min\left( \frac{\gamma_{m - 1}\left( {1 + {\gamma_{m}{\sum\limits_{j = 1}^{m - 1}\; p_{j}}}} \right)}{\gamma_{m}\left( {1 + {\gamma_{m - 1}{\sum\limits_{j = 1}^{m - 1}\; p_{j}}}} \right)} \right)}} = {{h\left( {{\sum\limits_{j = 1}^{m - 1}\; p_{j}} = 1} \right)} = \frac{\gamma_{m - 1}\left( {1 + \gamma_{m}} \right)}{\gamma_{m}\left( {1 + \gamma_{m - 1}} \right)}}} & (40)\end{matrix}$

In addition, if a condition expressed by the following Expression (41)is satisfied, the PF metric illustrated in Expression (36) becomes amonotonically decreasing function with respect to p_(m-1) in the case offixing p₁ to p_(m-2). In other words, p_(m-1)=0 is an optimal value. Inother words, it is most appropriate to allocate total power to the user#1 to a user #m−2 and the user #m.

$\begin{matrix}{{\frac{T_{m - 1}}{T_{m}} \geq {\max\left( \frac{\gamma_{m - 1}\left( {1 + {\gamma_{m}{\sum\limits_{j = 1}^{m - 1}\; p_{j}}}} \right)}{\gamma_{m}\left( {1 + {\gamma_{m - 1}{\sum\limits_{j = 1}^{m - 1}\; p_{j}}}} \right)} \right)}} = {{h\left( {{\sum\limits_{j = 1}^{m - 1}\; p_{j}} = 0} \right)} = \frac{\gamma_{m - 1}}{\gamma_{m}}}} & (41)\end{matrix}$

From the above, a condition of satisfying the above-mentioned Expression(11) is derived.

Returning to the description of FIG. 6, the allocation decision unit 34decides, as a “resource allocation target”, a terminal 50 or acombination of terminals, which corresponds to a PF metric whose valueis a maximum among PF metrics calculated in the metric calculation unit33.

The MCS decision unit 35 decides a coding rate, the number of modulationlevels, and adjusted power, which are to be applied to user dataaddressed to each of terminals 50 that serve as resource allocationtargets and that are decided in the allocation decision unit 34. Inaddition, the MCS decision unit 35 generates the scheduling informationand the control information, described above, and outputs the generatedscheduling information and control information to the corresponding userdata signal generation unit 11 and the control signal generation unit20, respectively.

Example of Configuration of Terminal

FIG. 8 is a block diagram illustrating an example of a terminal of thefirst embodiment. In FIG. 8, the terminals 50 each include a wirelessreception unit 51, an OFDM reception processing unit 52, ademultiplexing unit 53, a channel quality estimation unit 54, a controlsignal reception processing unit 55, a reception processing unit 56, anAck generation unit 57, a transmission processing unit 58, and awireless transmission unit 59.

The wireless reception unit 51 performs predetermined wireless receptionprocessing (down-conversion, analog-to-digital conversion, and so forth)on a wireless signal received via an antenna and outputs an obtainedOFDM signal to the OFDM reception processing unit 52.

The OFDM reception processing unit 52 forms a reception signal(corresponding to the above-mentioned multiplexed signal) from the OFDMsignal received from the wireless reception unit 51. As illustrated inFIG. 8, the OFDM reception processing unit 52 includes a CP removal unit61 and an FFT unit 62. The CP removal unit 61 removes a CP from the OFDMsignal received from the wireless reception unit 51 and outputs, to theFFT unit 62, the OFDM signal after removal of the CP. The FFT unit 62converts, from a signal in a time domain to a signal in a frequencydomain, the OFDM signal after removal of the CP and outputs the obtainedsignal in the frequency domain to the demultiplexing unit 53.

The demultiplexing unit 53 extracts signals of respective channels fromthe reception signal obtained in the OFDM reception processing unit 52and outputs the obtained signals of the respective channels tocorresponding functional units. The demultiplexing unit 53 outputs, forexample, a pilot signal of a pilot channel, included in the receptionsignal, to the channel quality estimation unit 54. In addition, thedemultiplexing unit 53 outputs, to the control signal receptionprocessing unit 55, a control signal of a control channel, included inthe reception signal. In addition, the demultiplexing unit 53 outputs,to the reception processing unit 56, a data signal of a data channel,included in the reception signal.

Based on the pilot signal received from the demultiplexing unit 53, thechannel quality estimation unit 54 performs estimation of channelquality and outputs, to the transmission processing unit 58, informationrelating to an obtained channel quality estimation value (in otherwords, channel state information (CQI, PMI, RI, and so forth)).

The control signal reception processing unit 55 demodulates the controlsignal received from the demultiplexing unit 53 and outputs controlinformation included in a demodulation result to the receptionprocessing unit 56. Note that, as described above, the controlinformation includes the identification information of each of usersserving as targets of the non-orthogonal multiplexing, the coding rateapplied to a user data signal addressed to each of the users, the numberof modulation levels, the adjusted power value, and so forth.

As illustrated in FIG. 8, the reception processing unit 56 includes acancellation unit 65, a demodulation unit 66, and a decoding unit 67. Inthe reception processing unit 56, first the demodulation unit 66 and thedecoding unit 67 perform demodulation processing and error correctiondecoding processing, respectively, on a signal addressed to anotherterminal 50 that is different from the device itself and that serves asa target of the non-orthogonal multiplexing and whose MCS is lower thanthe MCS of the device itself and is a minimum. In addition, in the caseof successful error correction decoding, the decoding unit 67 feedsback, to the cancellation unit 65, obtained reception data addressed tothe other terminal 50 different from the device itself. In addition, thecancellation unit 65 cancels the reception data received from thedecoding unit 67 from the data signal of the data channel received fromthe demultiplexing unit 53. The demodulation processing, the decodingprocessing, and the cancellation processing, described above, areperformed on all terminals 50 that are different from the device itselfand whose MCSs are lower than the MCS of the device itself. In addition,the demodulation unit 66 and the decoding unit 67 perform thedemodulation processing and the error correction decoding processing,respectively, on a data signal addressed to the device itself.

In the case where the decoding unit 67 succeeds in error correctiondecoding of the data signal addressed to the device itself, the Ackgeneration unit 57 generates and outputs an Ack signal to thetransmission processing unit 58 and in the case where the decoding unit67 fails in error correction decoding, the Ack generation unit 57generates and outputs a Nack signal to the transmission processing unit58.

The transmission processing unit 58 performs predetermined transmissionprocessing (encoding, modulation, and so forth) on an input signal andoutputs an obtained modulation signal to the wireless transmission unit59.

The wireless transmission unit 59 performs predetermined wirelesstransmission processing (digital-to-analog conversion, up-conversion,and so forth) on the modulation signal received from the transmissionprocessing unit 58 and transmits an obtained wireless signal via anantenna.

Example of Operation of Communication System

An example of a processing operation of the communication system 1having the above-mentioned configuration will be described. Here, inparticular, a selection method for a “metric calculation target”, basedon the selection unit 43 in the base station 10, will be described. FIG.9 to FIG. 11 are diagrams each made available for explaining a selectionmethod for a metric calculation target of the first embodiment. FIG. 9is related to a selection method for a metric calculation target forcombinations of terminals, each of the combinations of terminalsincluding two terminals 50, and FIG. 10 is related to a selection methodfor a metric calculation target for combinations of terminals, each ofthe combinations of terminals including three terminals 50. In addition,FIG. 11 is related to a selection method for a metric calculation targetfor combinations of terminals, each of the combinations of terminalsincluding m terminals 50 (m is a natural number greater than or equal tofour).

As described above, from among all the combinations of terminals, ineach of which the number of component terminals is up to N_(max) withinthe terminals 50-1 to 50-N_(S) serving as the “scheduling processingtargets”, the selection unit 43 selects, as the “metric calculationtargets”, combinations of terminals, which satisfy the “firstcondition”, and excludes combinations of terminals, which do not satisfythe “first condition”, from the “metric calculation targets”.

In accordance with a flow in, for example, FIG. 9, the selection unit 43selects a metric calculation target for combinations of terminals, eachof the combinations of terminals including two terminals 50.

In other words, the selection unit 43 sets, as an initial “determinationtarget”, one combination within a group of the combinations ofterminals, each of the combinations of terminals including two terminals50 (step S101).

The selection unit 43 sorts component terminals 50 of the setcombination of terminals serving as a determination target in descendingorder of instantaneous SNR (step S102).

The selection unit 43 determines whether or not the set combination ofterminals serving as a determination target satisfies the “firstcondition”, in other words, the above-mentioned Expression (9) (stepS103).

In the case where it is determined that the “first condition” issatisfied (step S103: affirmative), the selection unit 43 selects, as ametric calculation target, the combination of terminals serving as adetermination target (step S104). On the other hand, in the case whereit is determined that the “first condition” is not satisfied (step S103:negative), the selection unit 43 excludes, from metric calculationtargets, the combination of terminals serving as a determination target.In other words, the processing step proceeds to a step S105.

The selection unit 43 determines whether finishing setting allcombinations of terminals as determination targets or not (step S105),and in the case of not finishing setting (step S105: negative), theselection unit 43 sets a subsequent combination of terminals as adetermination target (step S106). In addition, a processing flow returnsto the step S102. In the case of finishing setting all combinations ofterminals as determination targets (step S105: affirmative), theprocessing flow in FIG. 9 is terminated.

Next, in accordance with a flow in FIG. 10, the selection unit 43selects a metric calculation target for combinations of terminals, eachof the combinations of terminals including three terminals 50.

In other words, the selection unit 43 sets, as an initial “determinationtarget”, one combination within a group of the combinations ofterminals, each of the combinations of terminals including threeterminals 50 (step S111).

The selection unit 43 sorts component terminals 50 of the setcombination of terminals serving as a determination target in descendingorder of instantaneous SNR (step S112).

The selection unit 43 determines whether or not the set combination ofterminals serving as a determination target satisfies the “firstcondition”, in other words, both the above-mentioned Expressions (9) and(10) (step S113).

In the case where it is determined that the “first condition” issatisfied (step S113: affirmative), the selection unit 43 selects, as ametric calculation target, the combination of terminals serving as adetermination target (step S114). On the other hand, in the case whereit is determined that the “first condition” is not satisfied (step S113:negative), the selection unit 43 excludes, from metric calculationtargets, the combination of terminals serving as a determination target.In other words, the processing step proceeds to a step S115.

The selection unit 43 determines whether finishing setting allcombinations of terminals as determination targets or not (step S115),and in the case of not finishing setting (step S115: negative), theselection unit 43 sets a subsequent combination of terminals as adetermination target (step S116). In addition, a processing flow returnsto the step S112. In the case of finishing setting all combinations ofterminals as determination targets (step S115: affirmative), theprocessing flow in FIG. 10 is terminated.

Next, in accordance with a flow in FIG. 11, the selection unit 43selects a metric calculation target for combinations of terminals, eachof the combinations of terminals including m terminals 50 (m is anatural number greater than or equal to four). This flow is repeatedlyperformed until m reaches N_(max).

In other words, the selection unit 43 sets, as an initial “determinationtarget”, one combination within a group of the combinations ofterminals, each of the combinations of terminals including m terminals50 (step S121).

The selection unit 43 sorts component terminals 50 of the setcombination of terminals serving as a determination target in descendingorder of instantaneous SNR (step S122).

The selection unit 43 determines whether or not the set combination ofterminals serving as a determination target satisfies the “firstcondition”, in other words, the above-mentioned Expression (11) (stepS123).

In the case where it is determined that the “first condition” issatisfied (step S123: affirmative), the selection unit 43 selects, as ametric calculation target, the combination of terminals serving as adetermination target (step S124). On the other hand, in the case whereit is determined that the “first condition” is not satisfied (step S123:negative), the selection unit 43 excludes, from metric calculationtargets, the combination of terminals serving as a determination target.In other words, the processing step proceeds to a step S125.

The selection unit 43 determines whether finishing setting allcombinations of terminals as determination targets or not (step S125),and in the case of not finishing setting (step S125: negative), theselection unit 43 sets a subsequent combination of terminals as adetermination target (step S126). In addition, a processing flow returnsto the step S122. In the case of finishing setting all combinations ofterminals as determination targets (step S125: affirmative), theprocessing flow in FIG. 11 is terminated.

As described above, according to the present embodiment, the basestation 10 is a base station to which the non-orthogonal multiple accessin which the terminals 50 are simultaneously allocatable to a commoncarrier is applied. In addition, in the, base station 10, from among allthe combinations of terminals serving as determination targets within agroup of the terminals 50 serving as the scheduling processing targets,the selection unit 43 selects, as the “metric calculation targets”,combinations of terminals, which satisfy the “first condition”, inaddition to the individual terminals 50 of the group of the terminals 50serving as the “scheduling processing targets”, and the selection unit43 excludes combinations of terminals, which do not satisfy the firstcondition, from the “metric calculation targets”.

According to the configuration of the base station 10, combinations ofterminals that do not satisfy the “first condition” are excluded fromthe “metric calculation targets”. Therefore, it is possible to reducethe number of metric calculation targets, and as a result, it ispossible to reduce a scheduling processing amount in the non-orthogonalmultiple access.

The above-mentioned “first condition” includes a condition that,regarding a combination of terminals including the first terminal 50 andthe second terminal 50, the first ratio (T₁/T₂) of a first averagethroughput T₁ of the first terminal 50 to a second average throughput T₂of the second terminal 50 is larger than the “first threshold value” andis smaller than the “second threshold value”.

According to the configuration of the base station 10, based on simpledetermination of whether or not the first ratio (T₁/T₂) falls within apredetermined range (a range larger than the first threshold value andsmaller than the second threshold value), it is possible to select ametric calculation target. From this, it is possible to reduce ascheduling processing amount in the non-orthogonal multiple access.

In addition, each of the above-mentioned “first threshold value” and“second threshold value” is a value based on a second ratio (γ₁/γ₂) of afirst instantaneous SNR γ₁ of the first terminal 50 to a secondinstantaneous SNR γ₂ of the second terminal 50.

Second Embodiment

In a second embodiment, before determining whether or not theabove-mentioned “first condition” is satisfied, it is determined whetheror not a “second condition” is satisfied. In addition, in the case wherethe “second condition” is not satisfied, a combination of terminalsserving as a determination target is excluded from metric calculationtargets. On the other hand, in the case where the “second condition” issatisfied, it is determined whether or not the “first condition” issatisfied. The “second condition” includes a condition that, regarding acombination of terminals including a first terminal and a secondterminal, the first ratio of the first average throughput of the firstterminal to the second average throughput of the second terminal islarger than “1”. Note that since being similar to that of the basestation 10 of the first embodiment, a basic configuration of a basestation of the second embodiment will be described with reference toFIGS. 5 to 7.

Example of Configuration of Base Station

In the base station 10 of the second embodiment, before determiningwhether or not the above-mentioned “first condition” is satisfied, theselection unit 43 determines whether or not the “second condition” issatisfied. In addition, in the case where the “second condition” is notsatisfied, the selection unit 43 excludes, from metric calculationtargets, a combination of terminals serving as a determination target.On the other hand, in the case where the “second condition” issatisfied, the selection unit 43 determines whether or not the “firstcondition” is satisfied.

The above-mentioned “second condition” is illustrated as follows.

In other words, in the case of two-user multiplexing, the “secondcondition” includes a condition that the following Expression (42) issatisfied.

$\begin{matrix}{\frac{T_{1}}{T_{2}} > 1} & (42)\end{matrix}$

In addition, in the case of the three-user multiplexing, the “secondcondition” includes a condition that both the above-mentioned Expression(42) and the following Expression (43) are satisfied.

$\begin{matrix}{\frac{T_{2}}{T_{3}} > 1} & (43)\end{matrix}$

In addition, in the case of the m-user multiplexing whose rank is higherthan or equal to four-user multiplexing, the “second condition” includesa condition that the following Expression (44) is satisfied.

$\begin{matrix}{\frac{T_{m - 1}}{T_{m}} > 1} & (44)\end{matrix}$

Here, a derivation process of the above-mentioned “second condition”will be described.

On Two-User Multiplexing

If paying attention to a first term and a second term other thanreciprocals of average throughputs in the above-mentioned Expression(14), the inequality expressed by Expression (45) may be acceptable.

$\begin{matrix}{\frac{\gamma_{1}}{1 + {p_{1}\gamma_{1}}} = {{\frac{1}{\gamma_{1}^{- 1} + p_{1}} \geq \frac{1}{\gamma_{2}^{- 1} + p_{1}}} = \frac{\gamma_{2}}{1 + {p_{1}\gamma_{2}}}}} & (45)\end{matrix}$

Accordingly, in the case where the following Expression (46) issatisfied, the following Expression (47) is satisfied.

$\begin{matrix}{{T_{1}/T_{2}} \leq 1} & (46) \\{\frac{\partial{g\left( p_{1} \right)}}{\partial p_{1}} \geq 0} & (47)\end{matrix}$

In other words, in the case where the above-mentioned Expression (46) issatisfied, the PF metric becomes a monotonically increasing functionwith respect to p₁ regardless of the instantaneous SNR.

Accordingly, at the time of calculating T₁/T_(z), it is determinedwhether or not a condition expressed by Expression (42) is satisfied,and in the case where the condition expressed by Expression (42) is notsatisfied, a combination of terminals serving as a determination targetmay be excluded from metric calculation targets. In addition to this, inthe case where the condition expressed by Expression (42) is satisfied,it may be determined whether or not the above-mentioned “firstcondition” is satisfied. From this, it is possible to reduce acalculation processing amount in selection processing.

On Three-User Multiplexing

If paying attention to a first term and a second term other thanreciprocals of average throughputs in the above-mentioned Expression(22), the inequality expressed by Expression (48) may be accepted.

$\begin{matrix}{\frac{\gamma_{2}}{1 + {\left( {p_{1} + p_{2}} \right)\gamma_{2}}} = {{\frac{1}{\gamma_{2}^{- 1} + \left( {p_{1} + p_{2}} \right)} \geq \frac{1}{\gamma_{3}^{- 1} + \left( {p_{1} + p_{2}} \right)}} = \frac{\gamma_{3}}{1 + {\left( {p_{1} + p_{2}} \right)\gamma_{3}}}}} & (48)\end{matrix}$

Accordingly, in the case where the following Expression (49) issatisfied, the PF metric becomes a monotonically increasing functionwith respect to p₂ regardless of the instantaneous SNR.

$\begin{matrix}{\frac{T_{2}}{T_{3}} \leq 1} & (49)\end{matrix}$

In addition, in the case where the following Expression (50) issatisfied, the PF metric becomes a monotonically increasing functionwith respect to p₁ regardless of the instantaneous SNR.

$\begin{matrix}{\frac{T_{1}}{T_{2}} \leq 1} & (50)\end{matrix}$

Accordingly, at the time of calculating T₁/T₂ and T₂/T₃, it isdetermined whether or not both Expression (42) and Expression (43) aresatisfied, and in the case where at least one of Expression (42) andExpression (43) is not satisfied, a combination of terminals serving asa determination target may be excluded from metric calculation targets.In addition to this, in the case where both Expression (42) andExpression (43) are satisfied, it may be determined whether or not theabove-mentioned “first condition” is satisfied. From this, it ispossible to reduce a calculation processing amount in the selectionprocessing.

m-User Multiplexing whose Rank Is Higher than or Equal to Four-UserMultiplexing

Using the above-mentioned Expression (37), based on the same kind ofthinking as those in cases of the two-user multiplexing and thethree-user multiplexing, it is possible to derive the conditionexpressed by the above-mentioned Expression (44). Accordingly, at thetime of calculating T₁/T₂ and T_(m)/T_(m-1), it is determined whether ornot Expression (37) is satisfied, and in the case where Expression (37)is not satisfied, a combination of terminals serving as a determinationtarget may be excluded from metric calculation targets. In addition tothis, in the case where Expression (37) is satisfied, it may bedetermined whether or not the above-mentioned “first condition” issatisfied. From this, it is possible to reduce a calculation processingamount in the selection processing.

Example of Operation of Base Station

An example of a processing operation of the base station 10 having theabove-mentioned configuration in the second embodiment will bedescribed. Here, in particular, a selection method for a “metriccalculation target”, based on the selection unit 43 in the base station10, will be described. FIG. 12 to FIG. 14 are diagrams each madeavailable for explaining a selection method for a metric calculationtarget of the second embodiment. FIG. 12 is related to a selectionmethod for a metric calculation target for combinations of terminals,each of the combinations of terminals including two terminals 50, andFIG. 13 is related to a selection method for a metric calculation targetfor combinations of terminals, each of the combinations of terminalsincluding three terminals 50. In addition, FIG. 14 is related to aselection method for a metric calculation target for combinations ofterminals, each of the combinations of terminals including m terminals50 (m is a natural number greater than or equal to four).

As described above, before determining whether or not theabove-mentioned “first condition” is satisfied, the selection unit 43 inthe base station 10 of the second embodiment determines whether or notthe “second condition” is satisfied. In addition, in the case where the“second condition” is not satisfied, the selection unit 43 excludes,from metric calculation targets, a combination of terminals serving as adetermination target. On the other hand, in the case where the “secondcondition” is satisfied, the selection unit 43 determines whether or notthe “first condition” is satisfied.

In accordance with a flow in, for example, FIG. 12, the selection unit43 selects a metric calculation target for combinations of terminals,each of the combinations of terminals including two terminals 50.

In other words, the selection unit 43 determines whether or not a setcombination of terminals serving as a determination target satisfies the“second condition”, in other words, the above-mentioned Expression (42)(step S201).

In the case where the condition of the above-mentioned Expression (42)is not satisfied (step S201: negative), the selection unit 43 excludes,from metric calculation targets, the combination of terminals serving asa determination target. In other words, the processing step proceeds tothe step S105. On the other hand, in the case where the condition of theabove-mentioned Expression (42) is satisfied (step S201: affirmative),the selection unit 43 performs the determination step in the step S103.

Next, in accordance with a flow in FIG. 13, the selection unit 43selects a metric calculation target for combinations of terminals, eachof the combinations of terminals including three terminals 50.

In other words, the selection unit 43 determines whether or not a setcombination of terminals serving as a determination target satisfies the“second condition”, in other words, both the above-mentioned Expression(42) and Expression (43) (step S211).

In the case where at least one of the above-mentioned Expression (42)and Expression (43) is not satisfied (step S211: negative), theselection unit 43 excludes, from metric calculation targets, thecombination of terminals serving as a determination target. In otherwords, the processing step proceeds to the step S115. On the other hand,in the case where both the above-mentioned Expression (42) andExpression (43) are satisfied (step S211: affirmative), the selectionunit 43 performs the determination step in the step S113.

Next, in accordance with a flow in FIG. 14, the selection unit 43selects a metric calculation target for combinations of terminals, eachof the combinations of terminals including m terminals 50 (m is anatural number greater than or equal to four). This flow is repeatedlyperformed until m reaches N_(max).

In other words, the selection unit 43 determines whether or not a setcombination of terminals serving as a determination target satisfies the“second condition”, in other words, the above-mentioned Expression (44)(step S221).

In the case where the condition of the above-mentioned Expression (44)is not satisfied (step S221: negative), the selection unit 43 excludes,from metric calculation targets, the combination of terminals serving asa determination target. In other words, the processing step proceeds tothe step S125. On the other hand, in the case where the condition of theabove-mentioned Expression (44) is satisfied (step S221: affirmative),the selection unit 43 performs the determination step in the step S123.

As described above, according to the present embodiment, in the basestation 10, regarding a combination of terminals including the firstterminal 50 and the second terminal 50, the selection unit 43 determineswhether or not the “second condition” of the first ratio (T₁/T₂) of thefirst average throughput T₁ of the first terminal 50 to the secondaverage throughput T₂ of the second terminal 50 being larger than “1” issatisfied. In addition, in the case where the second condition is notsatisfied, the selection unit 43 excludes, from metric calculationtargets, the combination of terminals serving as a determination target.In addition to this, in the case where the second condition issatisfied, the selection unit 43 determines whether or not theabove-mentioned first condition is satisfied.

According to this configuration of the base station 10, it is possibleto reduce a metric calculation processing amount.

Third Embodiment

A third embodiment is related to variations of a calculation method fora PF metric of a combination of terminals serving as a metriccalculation target. Note that a basic configuration of a base station ofthe third embodiment is similar to that of the base station 10 of thefirst embodiment or the second embodiment.

As illustrated in FIG. 15, in the base station 10 of the thirdembodiment, the metric calculation processing unit 42 includes a metriccalculation processing unit 151, a non-orthogonal multiplexing powercalculation unit 152, and a metric calculation processing unit 153. FIG.15 is a block diagram illustrating an example of a metric calculationunit that calculates a PF metric of a combination of terminals in thebase station of the third embodiment.

Regarding each of combinations of terminals serving as a “metriccalculation target” in user multiplexing whose rank is higher than orequal to the three-user multiplexing, the metric calculation processingunit 151 calculates a PF metric for each of candidates of powerdistribution and defines a PF metric whose value is a maximum among thecalculated PF metrics, as the PF metric of each of combinations ofterminals. In other words, regarding each of combinations of terminalsserving as a “metric calculation target” in user multiplexing whose rankis higher than or equal to the three-user multiplexing, the metriccalculation processing unit 151 performs processing similar to that ofthe metric calculation processing unit 42 of the first embodiment. Inother words, for example, an “iterative water-filling algorithm” of therelated art is used.

Regarding each of combinations of terminals serving as a “metriccalculation target” in the two-user multiplexing, using a firstderivative of a calculation function of the PF metric, thenon-orthogonal multiplexing power calculation unit 152 calculates apower value of the first terminal 50, which locally maximizes therelevant calculation function. In addition, using a condition that thesum of the power value of the first terminal 50 and a power value of thesecond terminal 50 is fixed, the power value of the second terminal 50is calculated. In other words, the non-orthogonal multiplexing powercalculation unit 152 finds an analytical solution of power.

Using, for example, the following Expression (51), the non-orthogonalmultiplexing power calculation unit 152 calculates the power value p₁ ofthe first terminal 50 and the power value p₂ of the second terminal 50.Expression (51) may be obtained by solving Expression (14) with respectto p₁ under the condition that the derivative illustrated in Expression(14) is “0”.

$\begin{matrix}{{p_{1} = \frac{{T_{1}\gamma_{2}} - {T_{2}\gamma_{1}}}{\gamma_{1}{\gamma_{2}\left( {T_{2} - T_{1}} \right)}}}{p_{2} = {1 - p_{1}}}} & (51)\end{matrix}$

Using power values of terminals 50 of each of combinations of terminals,calculated in the non-orthogonal multiplexing power calculation unit152, each of the combinations of terminals serving as a metriccalculation target, and the above-mentioned Expression (12), the metriccalculation processing unit 153 calculates the PF metric of each of thecombinations of terminals.

As described above, according to the present embodiment, in the basestation 10, regarding each of combinations of terminals serving as a“metric calculation target” in the two-user multiplexing, using a firstderivative of a calculation function of the PF metric, thenon-orthogonal multiplexing power calculation unit 152 calculates thepower value of the first terminal 50, which locally maximizes therelevant calculation function. In addition, using the power value of thefirst terminal 50, calculated in the non-orthogonal multiplexing powercalculation unit 152, the metric calculation processing unit 153calculates a PF metric.

According to this configuration of the base station 10, it is possibleto further reduce metric calculation.

Fourth Embodiment

A fourth embodiment is related to a selection method for a combinationof terminals serving as a metric calculation target and variations of acalculation method for a PF metric of a combination of terminals servingas a metric calculation target. Note that a basic configuration of abase station of the fourth embodiment is similar to that of the basestation 10 of the first embodiment or the second embodiment.

As illustrated in FIG. 16, in the base station 10 of the fourthembodiment, the metric calculation processing unit 42 includes metriccalculation processing units 251 and 252. In addition, the selectionunit 43 includes selection processing units 255 and 256. FIG. 16 is ablock diagram illustrating examples of a metric calculation processingunit and a selection unit in the base station of the fourth embodiment.

Using a method similar to that of the selection unit 43 in the firstembodiment or the second embodiment, the selection processing unit 255selects combinations of terminals serving as “metric calculationtargets” in user multiplexing whose rank is higher than or equal to thethree-user multiplexing.

Regarding each of combinations of terminals that serves as a “metriccalculation target” and that is selected in the selection processingunit 255, the metric calculation processing unit 251 performs processingsimilar to that of the metric calculation processing unit 42 of thefirst embodiment. In other words, for example, an “iterativewater-filling algorithm” of the related art is used.

Regarding each of combinations of terminals of the two-user multiplexingin the terminals 50-1 to 50-N_(S) serving as the “scheduling processingtargets”, using a first derivative of a calculation function of the PFmetric, the selection processing unit 256 calculates a power value ofthe first terminal 50, which locally maximizes the relevant calculationfunction. In other words, in accordance with the following Expression(52), the selection processing unit 256 calculates a power valuep_(1,tmp) of the first terminal 50, which locally maximizes thecalculation function.

$\begin{matrix}{p_{1,{tmp}} = \frac{{T_{1}\gamma_{2}} - {T_{2}\gamma_{1}}}{\gamma_{1}{\gamma_{2}\left( {T_{2} - T_{1}} \right)}}} & (52)\end{matrix}$

In addition, from among the combinations of terminals of the two-usermultiplexing in the terminals 50-1 to 50-N_(S) serving as the“scheduling processing targets”, the selection processing unit 256selects, as a “metric calculation target”, a combination of terminalsthat satisfies a “first condition” and excludes, from “metriccalculation targets”, a combination of terminals that does not satisfythe “first condition”.

This “first condition” is that the following Expression (53) issatisfied.

0<p _(1,tmp)<1  (53)

In addition, using the following Expression (54), the selectionprocessing unit 256 calculates power values of component terminals 50 ofa combination of terminals satisfying Expression (53). The calculatedpower values of the component terminals 50 are output to the metriccalculation processing unit 252.

p ₁ =p _(1,tmp)

p ₂=1−p ₁  (54)

Using power values of terminals 50 of each of combinations of terminals,the combinations of terminals being selected in the selection processingunit 256 and serving as metric calculation targets, and theabove-mentioned Expression (12), the metric calculation processing unit252 calculates the PF metric of each of the combinations of terminals.

As described above, according to the present embodiment, in the basestation 10, regarding the combination of terminals including twoterminals of the first terminal 50 and the second terminal 50, using thefirst derivative of the calculation function of the PF metric, theselection processing unit 256 calculates a power value of the firstterminal 50, which locally maximizes the relevant calculation function.In addition, while that the calculated power value of the first terminal50 is larger than “0” and is smaller than “1” is defined as the “firstcondition”, the selection processing unit 256 selects a metriccalculation target.

According to this configuration of the base station 10, it is possibleto further reduce a metric calculation processing amount.

Fifth Embodiment

In a fifth embodiment, by modifying the “first condition” described inthe first embodiment, “metric calculation targets” are further reduced.Note that since a basic configuration of a base station of the fifthembodiment is similar to that of the base station 10 of the firstembodiment, explanation will be performed with reference to FIGS. 5 to7.

In the base station 10 of the fifth embodiment, from among all thecombinations of terminals, in each of which the number of componentterminals is up to N_(max) within the terminals 50-1 to 50-N_(S) servingas the scheduling processing targets, the selection unit 43 selects, asthe “metric calculation targets”, combinations of terminals, whichsatisfy the “first condition”, and excludes combinations of terminals,which do not satisfy the “first condition”, from the “metric calculationtargets”.

This “first condition” is illustrated as follows.

In other words, in the case of the two-user multiplexing, the “firstcondition” includes a condition that the following Expression (55) issatisfied.

$\begin{matrix}{\frac{\gamma_{1}\left( {1 + {\alpha_{\max}\gamma_{2}}} \right)}{\gamma_{2}\left( {1 + {\alpha_{\max}\gamma_{1}}} \right)} < \frac{T_{1}}{T_{2}} < \frac{\gamma_{1}\left( {1 + {\alpha_{\min}\gamma_{2}}} \right)}{\gamma_{2}\left( {1 + {\alpha_{\min}\gamma_{1}}} \right)}} & (55)\end{matrix}$

Here, α_(max) and α_(min) are preliminarily decided setting values. Insuch a manner as, for example, α_(max)=0.99 and α_(min)=0.01, theα_(max) is set to a value smaller than “1” and close to “1” and theα_(min) is set to a value larger than “0” and close to “0”. In otherwords, in the case where, for example, p₁=0.01 or p₁=0.99 is an optimal,the PF metric is not expected to increase. Therefore, in the case wherepower is very unevenly distributed to component terminals 50 of acombination of terminals, the relevant combination of terminals isexcluded from metric calculation targets.

In addition, in the case of the three-user multiplexing, the “firstcondition” includes a condition that both the above-mentioned Expression(55) and the following Expression (56) are satisfied.

$\begin{matrix}{\frac{\gamma_{2}\left( {1 + {\alpha_{\max}\gamma_{3}}} \right)}{\gamma_{3}\left( {1 + {\alpha_{\max}\gamma_{2}}} \right)} < \frac{T_{2}}{T_{3}} < \frac{\gamma_{2}\left( {1 + {\alpha_{\min}\gamma_{3}}} \right)}{\gamma_{3}\left( {1 + {\alpha_{\min}\gamma_{2}}} \right)}} & (56)\end{matrix}$

In addition, in the case of the m-user multiplexing whose rank is higherthan or equal to the four-user multiplexing, the “first condition”includes a condition that the following Expression (57) is satisfied.

$\begin{matrix}{\frac{\gamma_{m - 1}\left( {1 + {\alpha_{\max}\gamma_{m}}} \right)}{\gamma_{m}\left( {1 + {\alpha_{\max}\gamma_{m - 1}}} \right)} < \frac{T_{m - 1}}{T_{m}} < \frac{\gamma_{m - 1}\left( {1 + {\alpha_{\min}\gamma_{m}}} \right)}{\gamma_{m}\left( {1 + {\alpha_{\min}\gamma_{m - 1}}} \right)}} & (57)\end{matrix}$

Note that if it is assumed that, in the above-mentioned Expression (55)to Expression (57), α_(max)=1 and α_(min)=0 are satisfied, the “firstcondition” illustrated in the first embodiment is obtained.

As described above, according to the present embodiment, the “firstthreshold value” is based on the second ratio of the first instantaneousSNR of the first terminal 50 to the second instantaneous SNR of thesecond terminal 50 and a predetermined first power value (in otherwords, α_(max)), the “second threshold value” is based on the secondratio and a predetermined second power value (in other words, α_(min)),and the predetermined first power value (α_(max)) is larger than thepredetermined second power value (α_(min)). In addition, thepredetermined first power value (α_(max)) is a value smaller than “1”and the predetermined second power value (α_(min)) is a value largerthan “0”.

According to this configuration of the base station 10, it is possibleto further narrow down combinations of terminals serving as metriccalculation targets. Therefore, it is possible to further reduce ametric calculation processing amount.

Sixth Embodiment

A sixth embodiment is related to an example in which the schedulingmethod described in one of the first embodiment to the fifth embodimentis applied to a combination of “beam forming” and NOMA. In other words,non-orthogonal multiplexing of users is performed in each beam. Notethat here a case in which the scheduling method described in, forexample, the first embodiment is applied to the combination of “beamforming” and NOMA will be described.

Example of Configuration of Base Station

FIG. 17 is a block diagram illustrating an example of a base station ofthe sixth embodiment.

In FIG. 17, user data signal generation units 311-1 to 311-N_(B)correspond to respective “beams” different from one another. In otherwords, the user data signal generation units 311-1-1 to 311-1-N_(max)correspond to respective terminals 450 serving as scheduling targetswithin one beam.

Upon receiving “scheduling information” from a scheduler 319, each ofthe user data signal generation units 311 generates a user data signal,based on the scheduling information. The “scheduling information”includes the number of modulation levels, a coding rate, and a powervalue.

Multiplexing units 12-1 to 12-N_(B) correspond to respective “beams”different from one another. For example, the multiplexing unit 12-1receives, in the same time period, user data signals from the up toN_(max) user data signal generation units 11, which correspond to a beam1, and multiplexes the received data signals.

A precoding unit 312 multiplies multiplexed signals, received from therespective multiplexing units 12-1 to 12-N_(B), by a precoding matrixdetermined in the scheduler 319 and outputs the obtained multiplexedsignals subjected to precoding to channel multiplexing units 13-1 to13-N_(AT).

The channel multiplexing units 13-1 to 13-N_(AT) correspond torespective antennas different from one another. In addition, OFDMtransmission processing units 14-1 to 14-N_(AT) correspond to therespective antennas different from one another. In addition, wirelesstransmission units 15-1 to 15-N_(AT) correspond to the respectiveantennas different from one another.

As illustrated in FIG. 18, the scheduler 319 includes a metriccalculation unit 333, an allocation decision unit 334, and an MCSdecision unit 335. As illustrated in FIG. 19, the metric calculationunit 333 includes per-matrix metric calculation units 341-1 to341-N_(CB). FIG. 18 is a block diagram illustrating an example of ascheduler of the sixth embodiment. FIG. 19 is a block diagramillustrating an example of a metric calculation unit of the sixthembodiment.

The per-matrix metric calculation units 341-1 to 341-N_(CB) correspondto respective precoding matrices different from one another. In otherwords, in the base station 310, N_(CB) precoding matrices are preparedin advance. Each of the per-matrix metric calculation units 341calculates a PF metric per precoding matrix. Here, the terminals 450serving as “scheduling processing targets” of each of the per-matrixmetric calculation units 341 are terminals 450 in which the precodingmatrix corresponding to each of the per-matrix metric calculation units341 is fed back as a “desired precoding matrix”.

In addition, as illustrated in FIG. 19, each of the per-matrix metriccalculation units 341 includes per-beam metric calculation units 342-1to 342-N_(B) and a per-matrix metric calculation processing unit 343.

The individual per-beam metric calculation units 342 calculaterespective PF metrics for respective combinations of a precoding matrixand a beam, different from one another.

In addition, as illustrated in FIG. 19, each of the per-beam metriccalculation units 342 includes metric calculation processing units 351and 352, a selection unit 353, and a maximum metric selection unit 354.

Basically, the metric calculation processing units 351 and 352 and theselection unit 353 have the same functions as those of the metriccalculation processing units 41 and 42 and the selection unit 43,respectively, of the first embodiment. In this regard, however, theterminals 450 serving as “scheduling processing targets” in the metriccalculation processing units 351 and 352 and the selection unit 353 areterminals 450 in which the precoding matrix corresponding to each of theper-matrix metric calculation units 341 is fed back as a “desiredprecoding matrix”.

Regarding one combination of a precoding matrix and a beam, the maximummetric selection unit 354 selects a maximum PF metric from among PFmetrics calculated in the metric calculation processing units 351 and352. In addition, the maximum metric selection unit 354 outputs theselected PF metric to the per-matrix metric calculation processing unit343.

The per-matrix metric calculation processing unit 343 calculates the sumof PF metrics (in other words, PF metrics in units of beams) receivedfrom the corresponding per-beam metric calculation units 342-1 to342-N_(B) (in other words, a PF metric per matrix), and the per-matrixmetric calculation processing unit 343 outputs the calculated sum to theallocation decision unit 334.

Returning to the description of FIG. 18, the allocation decision unit334 decides, as “resource allocation targets”, a precoding matrix andterminals 450 or a combination of terminals within a beam, whichcorrespond to a PF metric whose value is a maximum among PF metricsreceived from the per-matrix metric calculation units 341-1 to341-N_(CB).

The MCS decision unit 335 decides a coding rate, the number ofmodulation levels, and an adjusted power to be applied to user dataaddressed to each of the terminals 450 serving as a resource allocationtarget decided in the allocation decision unit 334. In addition, the MCSdecision unit 335 generates the above-mentioned scheduling informationand control information and outputs the generated scheduling informationand control information to a corresponding one of the user data signalgeneration units 311 and the control signal generation unit 20,respectively. In addition, the MCS decision unit 335 outputs, to theprecoding unit 312, the precoding matrix serving as a resourceallocation target decided in the allocation decision unit 334.

Example of Configuration of Terminal

FIG. 20 is a block diagram illustrating an example of a terminal of thesixth embodiment. In FIG. 20, each of the terminals 450 includes aspatial filter unit 451, a control signal reception processing unit 455,a channel quality estimation unit 454, and a reception processing unit456. In FIG. 20, sets of the wireless reception units 51, the OFDMreception processing units 52, and the demultiplexing units 53 areprovided so as to be equal to the number of antennas.

The channel quality estimation unit 454 calculates (estimates) aprecoding matrix desired by the device itself and a channel qualityestimation value of each of beams in the case where the relevant desiredprecoding matrix is applied. In addition, the channel quality estimationunit 454 outputs, to the transmission processing unit 58, the desiredprecoding matrix and the channel quality estimation value of each ofbeams.

The control signal reception processing unit 455 demodulates a controlsignal received from the demultiplexing unit 53 and outputs, to thereception processing unit 56, control information included in ademodulation result. The control information includes informationindicating an actually applied precoding matrix, identificationinformation of each of users serving as targets of the non-orthogonalmultiplexing within each of beams, and a coding rate, the number ofmodulation levels, and an adjusted power value that are applied to auser data signal addressed to each of users. Note that in the case ofusing a specific pilot, the information indicating the precoding matrixdoes not have to be included in the control information.

Using, for example, a minimum mean square error (MMSE), the spatialfilter unit 451 separates the beams.

In the reception processing unit 456, in a beam signal including asignal addressed to the device itself, the demodulation unit 66 and thedecoding unit 67 perform demodulation processing and error correctiondecoding processing, respectively, on a signal addressed to anotherterminal 450 that is different from the device itself and that serves asa target of the non-orthogonal multiplexing and whose MCS is lower thanthe MCS of the device itself and is a minimum. In addition, in the caseof successful error correction decoding, the decoding unit 67 feedsback, to the cancellation unit 65, obtained reception data addressed tothe other terminal 450 different from the device itself. In addition,the cancellation unit 65 cancels the reception data received from thedecoding unit 67 from the beam signal including the signal addressed tothe device itself. The demodulation processing, the decoding processing,and the cancellation processing, described above, are performed on allterminals 450 that are different from the device itself and whose MCSsare lower than the MCS of the device itself. In addition, thedemodulation unit 66 and the decoding unit 67 perform the demodulationprocessing and the error correction decoding processing, respectively,on a data signal addressed to the device itself.

By doing in such a manner as described above, even in the case where the“beam forming” and the non-orthogonal multiple access are combined, itis possible to reduce the number of metric calculation targets and as aresult, it is possible to reduce a scheduling processing amount in thenon-orthogonal multiple access.

Another Embodiment

Individual component elements in each of units illustrated in theembodiments do not have to be physically configured as illustrated indrawings. In other words, a specific example of the distribution orintegration of the individual units is not limited to one of examplesillustrated in drawings, and the individual units may be configured byfunctionally or physically integrating or distributing all or part ofthe individual units in arbitrary units according to various loads,various statuses of use, and so forth.

Furthermore, all or arbitrary part of various kinds of processingfunctions performed in each of devices may be performed on a centralprocessing unit (CPU) (or a microcomputer such as a micro processingunit (MPU) or a micro controller unit (MCU)). In addition, all orarbitrary part of various kinds of processing functions may be performedon a program analyzed and performed on a CPU (or a microcomputer such asan MPU or a MCU) or may be performed on hardware based on hard-wiredlogic.

The base station and the terminals of one of the first embodiment to thesixth embodiment may be realized by, for example, the following hardwareconfiguration.

FIG. 21 is a diagram illustrating of an example of a hardwareconfiguration of a base station. As illustrated in FIG. 21, a basestation 500 includes a radio frequency (RF) circuit 501, a processor502, a memory 503, and a network interface (IF) 504. As an example ofthe processor 502, a central processing unit (CPU), a digital signalprocessor (DSP), a field programmable gate array (FPGA), or the like maybe cited. In addition, as an example of the memory 503, a random accessmemory (RAM) such as a synchronous dynamic random access memory (SDRAM),a read only memory (ROM), a flash memory, or the like may be cited. Eachof the base stations of the first embodiment to the sixth embodiment hasa configuration illustrated in FIG. 21.

In addition, a processor included in an amplifying device may performprograms stored in various kinds of memories such as non-volatilestorage media, thereby realizing various kinds of processing functionsperformed in the base station of one of the first embodiment to thesixth embodiment. In other words, programs corresponding to individualprocessing operations performed by the user data signal generation units11 and 311, the multiplexing unit 12, the channel multiplexing unit 13,the OFDM transmission processing unit 14, the reception processing unit17, the extraction unit 18, the schedulers 19 and 319, the controlsignal generation unit 20, and the precoding unit 312 may be recorded inthe memory 503 and the individual programs may be executed by theprocessor 502. In addition, the wireless transmission unit 15 and thewireless reception unit 16 are realized by the RF circuit 501.

Note that while here explanation is performed under the assumption thatthe base station 500 is an integrated device, the base station 500 isnot limited to this. For example, the base station 500 may be configuredby two separated devices of a wireless device and a control device. Inthis case, the RF circuit 501 is arranged in, for example, the wirelessdevice, and the processor 502, the memory 503, and the network IF 504are arranged in, for example, the control device.

FIG. 22 is a diagram illustrating of an example of a hardwareconfiguration of a terminal. As illustrated in FIG. 22, a terminal 600includes an RF circuit 601, a processor 602, and a memory 603. Each ofthe terminals of the first embodiment to the sixth embodiment has theconfiguration illustrated in FIG. 22.

As an example of the processor 602, a CPU, a DSP, an FPGA, or the likemay be cited. In addition, as an example of the memory 603, a RAM suchas an SDRAM, a ROM, a flash memory, or the like may be cited.

In addition, a processor included in an amplifying device may performprograms stored in various kinds of memories such as non-volatilestorage media, thereby realizing various kinds of processing functionsperformed in the terminals of the first embodiment to the sixthembodiment. In other words, programs corresponding to individualprocessing operations performed by the OFDM reception processing unit52, the demultiplexing unit 53, the channel quality estimation units 54and 454, the control signal reception processing units 55 and 455, thereception processing units 56 and 456, the Ack generation unit 57, thetransmission processing unit 58, and the spatial filter unit 451 may berecorded in the memory 603 and the individual programs may be executedby the processor 602. In addition, the individual processing operationsperformed by the OFDM reception processing unit 52, the demultiplexingunit 53, the channel quality estimation units 54 and 454, the controlsignal reception processing units 55 and 455, the reception processingunits 56 and 456, the Ack generation unit 57, the transmissionprocessing unit 58, and the spatial filter unit 451 may be divided andperformed by processors such as a baseband CPU and an application CPU.In addition, the wireless reception unit 51 and the wirelesstransmission unit 59 are realized by the RF circuit 601.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A base station comprising: a memory; and aprocessor coupled to the memory and configure to: when scheduling aplurality of terminals based on non-orthogonal multiple access in whicha same radio resource having a same time and a same frequency isallocable to two or more terminals of the plurality of terminals,calculate each metric of each of selected terminal combinations and eachterminals of the plurality of terminals, each of the selected terminalcombinations including two or more terminals of the plurality ofterminals, and determine to allocate each radio resource to each of theselected terminal combinations and each terminals of the plurality ofterminals based on each metric, wherein the selected terminalcombinations are obtained by selecting, from among all terminalcombinations of the plurality of terminals, each terminal combinationthat satisfies a first condition.
 2. The base station according to claim1, wherein for a terminal combination including N terminals (N being anatural number more than 1), the first condition is that a throughputratio of m-1th throughput to mth throughput is more than a firstthreshold value and less than a second threshold value for each m(2≦m≦N), the m-1th throughput being a throughput of m-1th terminal whosechannel quality is m-1th highest in the N terminals, the mth throughputbeing a throughput mth terminal whose channel quality is mth highest inthe N terminals.
 3. The base station according to claim 2, wherein eachof the first threshold value and the second threshold value is obtainedbased on a channel quality ratio of m-1th channel quality of the m-1thterminal to mth channel quality of the mth terminal.
 4. The base stationaccording to claim 3, wherein the first threshold value is obtainedfurther based on a first transmission power value, the second thresholdvalue is obtained further based on a second transmission power valuethat is less than the first transmission power value.
 5. The basestation according to claim 1, wherein for a terminal combinationincluding N terminals (N being a natural number more than 1), theselected terminal combinations are obtained by selecting, from among allterminal combinations of the plurality of terminals, each terminalcombination that satisfies a second condition and further satisfies thefirst condition, the second condition being that a throughput ratio ofm-1th throughput to mth throughput is more than 1 for each m (2≦m≦N),the m-1th throughput being a throughput of m-1th terminal whose channelquality is m-1th highest in the N terminals, the mth throughput being athroughput mth terminal whose channel quality is mth highest in the Nterminals.
 6. The base station according to claim 1, wherein for aterminal combination including 2 terminals, the first condition is thata specified transmission power value is more than 0 and less than 1, thespecified transmission power value being a transmission power value of aspecified terminal of the 2 terminals, the specified transmission powervalue being obtained based on a local maximum of a function forcalculating each metric.
 7. The base station according to claim 1,wherein the selected terminal combinations are obtained by excluding,from among all terminal combinations of the plurality of terminals, eachterminal combination that does not satisfy the first condition.
 8. Thebase station according to claim 2, wherein each channel quality is asignal to noise ratio (SNR).
 9. A resource allocation method comprising:when scheduling a plurality of terminals based on non-orthogonalmultiple access in which a same radio resource having a same time and asame frequency is allocable to two or more terminals of the plurality ofterminals, calculating each metric of each of selected terminalcombinations and each terminals of the plurality of terminals, each ofthe selected terminal combinations including two or more terminals ofthe plurality of terminals; and determining to allocate each radioresource to each of the selected terminal combinations and eachterminals of the plurality of terminals based on each metric, whereinthe selected terminal combinations are obtained by selecting, from amongall terminal combinations of the plurality of terminals, each terminalcombination that satisfies a first condition.